Smart cards (also referred to as chip cards or ICCs (integrated circuit card)) can be found in a variety of applications, for example as reliable portable means of identification, authentication or as portable means for data storage or data processing. Due to their practicality and the resulting applicability in various technical fields, their performance and usability have been constantly improved. One such improvement may be seen in the provision of contactless smart cards which do not have to be inserted into a reader during use but can, for example, remain in a wallet which, together with the respective contactless smart card to be contacted tucked inside, may be placed on a contact field of the reader or can be swiped past the reader. There are also dual-interface chip cards available, which offer both a contact based interface, such as the standard chip card interface as defined by the ISO/IEC 7816-2 standard, and a contactless interface, which is usually provided by a chip card antenna.
In contactless smart cards, magnetic fields are used to supply the card with power and to exchange data between the smart card and the reader. The energy which is needed to power the processor or microcontroller circuit which may be provided on the chip card in the form of a chip or other circuits/components is drawn from the magnetic field provided by the reader. Therefore, a contactless microcontroller which is coupled to one antenna may be provided in the smart card in order to supply energy to external components of the smart card and to the main microcontroller or processor of the smart card. Since the whole system including the chip card and optional external components, such as a keyboard, various sensors or a display, is then supplied with power via one interface of the single contactless microcontroller, an interdependency or interference between the different processes may be present, for example between the process of contactless communication, the execution or operation of the main microcontroller of the smart card and the supply of external components with power. Area optimized input structures on the smart card may even make it impossible to supply external components with power, as the surplus system current is shunted via an internal VDD shunt to save chip area.